Gasar (device for gas amplification by stimulated emission and radiation)



June 21, 1966 w, ROBERTS 3,257,620

GASAR (DEVICE FOR GAS AMPLIFICATION BY STIMULATED EMISSION AND RADIATION) 4 Sheets-Sheet 1 Filed March 19, 1962 INVENTOR.

June 21, 1966 Filed March 19, 1962 L. GASAR (DEVICE FOR GAS AMPLIFICATION BY STIMUL EMISSION AND RADIATION) W. ROBERTS II IH 126' IIII I IIII IIII I I II I I I I A28 ATED 4 Sheets-Sheet 3 QI a EI IHIIHIIII "TIIIIILL .II III HIIHII 'INVENTOR I II I II June 21, 1966 L. w. ROBERTS GASAR (DEVICE FOR GAS AMPLIFICATION BY STIMULATED EMISSION AND RADIATION) 4 Sheets-Sheet 4 Filed March l9, 1962 INVENTOR. ozguw @fllw 3,257,620 GASAR (DEVICE FOR GAS AMPLIFICATION BY STIMULATED EMISSION AND RADIATION) Louis W. Roberts, Wakefield, Mass., assignor to Metcom,

, Inc., Salem, Mass., a corporation of Delaware Filed Mar. 19, 1962, Ser. No. 180,795 8 Claims. (Cl. 330-4) The present invention relates to radio frequency electromagnetic wave amplifiers, more particularly it relates to.

radars, electronic countermeasure equipment, and numerous other applications in both military and civilian activities.

Earlier kilomegacycle wave generators and amplifiers depend broadly upon the modulation of motion of electrons in an electron stream. Each of these earlier devices utilizes a technique for controlling the coherent kilomegacycle wave generation; however, each of these earlier techniques for controlling the motion of electrons imposes some limitation on the wave generator. For instance, the klystronmodulates the velocity of a stream of electrons contained within a high vacuum tube by an alternating electrical charge which commonly is carried on electrodes through which the electron stream passes. The electromagnetic wave which accompanies the moving stream of electrons is coupled to a tunable resonant cavity and by this coupling the waves are made available for application exterior to the klystron tube. For reasons inherent in the alternating electrical charge technique of velocity modulating the electron stream, the klystron is limited in its adaptability to higher frequencies and frequency band width. The magnetron utilizes a velocity modulated electron stream wherein electrons are induced to yield energy to an accompanying electromagnetic wave traveling at less than its free space velocity, by reason of coupling the wave to one or more precision cavities. The length of the trajectory of the electrons in a magnetron is greatly extended by confining the electron beam trajectory to a circular path with a strong focusing magnetic field. The magnetron is capable of delivering waves of much higher peak power than the'klystron, but only within a yet narrower frequency band; the magnetron frequency cannot be conveniently altered. Traveling wave tubes utilize a velocity modulate, focused electron beam which interacts with an electromagnetic wave propagated along a helix which is parallel with the electron stream at less than free space velocity. The Wave is United States Patent slowed by coupling with the helical structure. The traveling wave tube depends upon synchronizing, by means of the helix, the velocity and phase of the electromagnetic wave with the velocity and instantaneous position of the density waves in the electron stream. The traveling wave tube possesses advantages over klystrons and magnetrons with respect to tunability and broad band performance; however, the traveling wave tube possesses the disadvantages of being expensive and often difficult to operate at the desired power level. None of the above are, strictly speaking, electron plasma tubes; all operate from an electron beam in a hard vacuum (that is, in vacuum below 10- mm. Hg) and all depend upon carefully focusing the electron beam to facilitate modulation of the velocity of electrons in the beam.

Another kilomegacycle device which is properly termed a plasma tube utilizes, for obtaining amplification, injection of a focused electron beam into a plasma. A signal coupled to the incoming beam traverses the plasma; an output signal is extracted from the electron beam after waves on the electron beam have extracted energy from the plasma. Such a device, while it utilizes a plasma field, remains for its operation, dependent upon a focused electron beam; and accordingly is limited by the focus of the electron beam in a plasma.

There is, then, a continuing need for an improved megacycle wave generator or amplifier which is capable of large power output, broad frequency band performance, low'noise characteristics, simple in structure and inexpensive to construct, and requiring a minimum of external circuitry or external adjustment to achieve and maintain proper performance. In particular, there is need for a broad band high power, high kilomegacycle frequency amplifier which is not subject to the limitations in operation which characterize the earlier devices referred to above.

My invention adopts a hitherto unused mechanism for electromagnetic wave amplification to an entirely novel kilomegacycle wave amplifier device.

In a plasma, that is, an intensely ionized gaseous atmosphere, free electrons move' at velocities which are a function of the temperature of the electron. Stated in other terms, the total kinetic energy or temperature of the electron is the sum of the components of the kinetic energy of translation. The distribution of velocity, and therefore the distribution of electron temperature in a steady state plasma, is described by the relative probability of an electron having a given velocity or given temperature. Expressed as a distribution function, f(v), the velocity v, the usual Maxwell velocity distribution function discussed in numerous physics texts may be represented as:

where,

m=mass of electron k Boltzmans constant, 1.38 1O- erg/ k T=temperature in K Hence, the average kinetic energy is:

/2 mv %kT In the Maxwellian distribution case, the incoherent electron radiation temperature, T7, is assumed to be identical to the statistical mean electron temperature T that is:

The earlier kilomegacycle wave generating devices referred to above all utilize radiation mechanisms wherein the stream of electrons is modulated, but at all times the electrons are characterized as having a Maxwellian velocity (or temperature) distribution. My invention utilizes radiation mechanisms which are operative only in :a plasma with free electrons in a non-Maxwellian velocity (or temperature) distribution; that is in my invention the relationship between the incoherent radiation temperature T'y and the statistical mean electron temperature T may be described by the inequality:

with the greater inequality near the input of the tube. Thus, in a non-Maxwellian velocity distribution of electrons in a plasma, a negative radiation temperature and a negative radiation absorption coefficient may be brought about. Electron plasmas having a negative radiation absorption characteristic may, by radiation mechanisms, discussed below, amplify an incident wave with stimulated emission by electrons as the wave propagates through the plasma. Specific mechanisms in which wave amplification within a plasma field may be observed are described in:

Emission of Radio Frequency Waves from Plasmas, G. Bekefi and Sanborn C. Brown, American Journal of Physics, vol. 29, No. 7, 404-428, July 1961;

Kirchoffs Radiation Law for Plasmas with Non-Maxwellian Distributions, G. Bekefi, Jay L. Hirshfield and Sanborn C. Brown, The Physics of Fluids, vol. 4, No. 2, February 1961;

Incoherent Microwave Radiation from a Plasma in a Magnetic Field, Jay L. Hirshfield and Sanborn C.

Brown, Physical Review, vol. 122, No. 3, 719725, May 1,

Cyclotron Radiation from a Hot Plasma, Jay L. Hirshfield, D. E. Baldwin and Sanborn C. Brown, The Physics of Fluids, vol. 4, No. 2, February 1961;

Cyclotron Emission from Plasmas with Non-Maxwelli-an Distributions, G. Bekefi, Jay L. Hirshfield and Sanborn C. Brown, Physical Review, vol. 122, No. 4, 1037 1042, May 15-, 1961.

In Bremsstrahlung radiation, the radiation orginates from collisions of electrons with atoms or ions. For a plasma possessing the appropriate negative radiation absorption characteristic, irradiated by a weak intensity wave, the resulting collisions of electrons with gaseous atoms and ions are a function of the incident radiation frequency, w, and the density, N, of the atoms or ions in the plasma. For high frequency incident radiation, or for low values of N, the emitted radiation varies proportionately to Qm(N), the cross section for spontaneous emission of radiation of energy lm (for one polarization of the wave by an electron of velocity v), Where [1 is Plancks constant. At low frequencies, or high values of N, the emitted radiation varies as V Q m(V). The Bremsstrahlung mechanism is most significant, then, at lower incident radiation frequencies and higher collision frequencies.

In the presence of a magnetic field, electrons radiate as a result of their orbital motion. This mechanism of radiation is termed cyclotron radiation. A related radiation mechanism is termed synchrotron radiation and originates from harmonics of the cyclotron frequency. At higher electromagnetic wave frequencies, high to, and at lower collision frequencies, low N, the cyclotron and synchrotron radiation mechanisms are more significant.

The plasma radiation mechanisms are a function of parameters which may be controlled by gross adjustments of the plasma such as statistical temperature distribution, density, and incident wave frequency. Because of these features my plasma amplifying devices are well suited to millimeter wave generation and amplification for the reason that the output frequency does not depend upon electron transit time, or the dimensions of cavities or the geometrical relationships of small component parts within the device.

In accordance with Kirchhoffs law, a system exhibiting stimulated emission which exceeds stimulated absorption may be described as having a negativ radiation temperature. Electromagnetic waves propagated through a plasma having a negative radiation temperature can be amplified in traversing the plasma. The amplification mechanism thus lends itself to great flexibility of frequency band width and power capacity without the limitations imposed by complex and mechanically fragile physical structures.

In a specific instance, more than one radiation mechanismmay be operative at one instant and for a particular circumstance, hence, a quantitative analysis of the entire radiation and amplification process in a specific embodiment of my invention may be extremely complex. On the other hand, the mathematical analyses of various radiation mechanisms operable within an electron plasma have been described in the technical references cited above and other technical literature. These analyses are readily extended to the case of a non-Maxwellian electron velocity distribution.

Accordingly, one object of my invention is to provide a high frequency electromagnetic wave amplifier which utilizes a non-Maxwellian velocity distribution of electrons having a negative radiation absorption characteristic.

Another object of my invention is to provide a kilomegacycle wave amplifier utilizing an electron plasma.

Another object of my invention is to provide a simple broad band radio frequency wave amplifier.

Another object of my invention is to provide a high power capacity radio frequency wave amplifier.

Another object of my invention is to provide an amplifier device which does not require a complex wave propagating structure which must be cooled and which is often expensive to fabricate.

Yet another object of my invention is to provide a radio frequency amplifier adaptable to performance in millimeter Wave lengths.

Another object of my invention is to provide a broad band, high power capacity radio frequency amplifier which does not require complex external controls for its operatron.

Still another object of my invention is to provide a broad band, hi h power capacity radio frequency amplifier which does not require close tolerance mechanical structures to control frequency.

Another object of my invention is to provide a low noise broad band radio frequency wave amplifier.

Still another object of my invention is to provide a radio frequency wave generator which does not require a magnetically focused electron beam, but one which operates without regard to the orientation or geometry of an electron stream.

These and other objects and advantages of my invention will be apparent from the following drawings, specifications, and claims.

My invention, in a broad sense, is a device for amplifying radio frequency waves comprising the combination of an electron plasma, in which means have induced a non-Maxwellian electron velocity distribution, and structural means for passing radio frequency waves through and about the electron plasma, whereby energy in the electron plasma is transferred to and amplifies the radio frequency waves. My invention is further disclosed and illustrated in the accompanying drawings, wherein:

FIGURE 1 is a perspective view of one preferred embodiment of my invention adapted for use with rectangular wave guide.

FIGURE 2 is a longitudinal cross section view of the embodiment of my invention shown in FIGURE 1.

FIGURE 3 is a transverse section, taken on line 33, of the embodiment of my invention shown in FIGURES 1 and 2.

FIGURES 4 and 5 illustrate two variations in the embodiment of my invention illustrated in FIGURES 1 to 3. FIGURES 4 and 5 are transverse cross sections for separate embodiments of my invention adapted for ridge wave guide taken in the mid-portion of my device similarly to the transverse section shown in FIGURE 3.

FIGURE 6 is a longitudinal cross section view illustrating a second preferred embodiment of my invention adapted to flexible coaxial wave guide.

FIGURE 7 is a longitudinal cross section view illustrating yet another preferred embodiment of my invention adapted to rigid coaxial wave guide.

FIGURE 8 is a transverse cross section taken on line 88 in the embodiment of my invention illustrated in FIGURE 7.

Referring now to the drawings, FIGURES 1, 2 and 3 illustrate various features of a first preferred embodiment of my invention adapted for use with conventional rectangular wave guide. The rectangular wave guide 10 is provided with a section indicated at 12 of parallel offset contour so that a dielectric tube 14 may be passed longitudinally through the parallel offset section 12 of the wave guide. The tube 14 is constructed of a high melting point glass or quartz tube.- The cross section of the tube 14 is shown as circular, which is convenient but not a requirement. The length of the dielectric tube is sufficiently long to extend beyond 'the wave guide parallel offset section 12 at either end of the tube 14; this provides a convenient way of mounting the tube symmetrically within the interior of the wave guide parallel offset section and a convenientway of obtaining access to the tube 14 for the electrical conductors, described below, which must be passed into the interior of the tube. A first end 16 of the tube 14 containing an anode, described below, is mounted through an aperture 18 in a plane dielectric panel 20 which in turn is mounted in one face 22 of a portion of wave guide connecting the rectangular wave guide 10 to the offset parallel section 12. The second end 24 of the tube 14 contains a cathode, which is described below. The tube 14 is mounted through an aperture 26 in a dielectric panel 28 which in turn is mounted in the face 30 shown in the illustration of the wave guide connecting the rectangular wave guide 10 tothe parallel olfset wave guide section 12.

A cathode 3-2, mounted in the extreme end 24 of the tube 14, is connected to the tube exterior by leads 34 and 36; It is convenient to place the cathode 32, which has larger transverse dimensions than the dimension of the tube diameter, in a portion 38 of the tube having an enlarged diameter. It is desirable that the cathode provide .a relatively free electron source, and this may be accomplished by increased cathode dimensions. -An anode or plate 40 is mounted in the extreme end 16 of the tube and connected to the exterior of the tube with lead 42. Two-screen grids 44 and 46 connected to the exterior of the tube 14 by means of leads 48 and 50 are mounted in the'tube at spaced distances from the cathode 3'2 and from one another.

A cylindrical solenoid 52, which is adapted to provide a magnetic field, the lines of which cross at right angles to the electron paths between cathode 32 and anode 40, is mounted about the parallel offset wave guide section 12. The solenoid 52 is powered through leads 56 and 58. The orientation of the resulting magnetic field vector may be either toward the cathode 32 or the plate 40 for proper operation of my device. In FIGURE 1, the solenoid 52 is positioned to orient the resultant magnetic field vector toward the plate 40. A water jacket 54 for cooling the waveguide .12 and the solenoid 52 is provided about the inner diameter and ends of the solenoid. Coolant is circulated into and out of the water jacket 54 through conduits 60 and 6-2, respectively. FIGURE 3 best illustrates the concentric arrangement of the dielectn'c tube 14 within the wave guide 12; the wave guide Electrons introduced into the tube from the cathode 32 are accelerated through the screen grids 44 .and 46 and collected on the plate 40.

noid. By proper adjustment of the magnetic field strength,

which is accomplished by varying the solenoid current,

and adjustment of the plasma or electron density, which is accomplished by varying the cathode current and the plate voltage, and, finally, by varying the grid voltage, the electron velocity distribution in the tube may be appropriately adjusted and made to be a non-Maxwellian velocity distribution. Radio frequency waves incident on the plasma in which the non-Maxwellian electron velocity has been obtained may be amplified by extracting energy from the plasma and may then bep-ropa-gated along and through the wave guide. The dimensions and relative proportions of the device described and illustrated above may be varied widely and yet come within the necessary operating relation-ships. One specific model adapted to x-band or three centimeter rectangular wave guide employed a quartz tube approximately 18 inches long and inch in inside diameter. The cathode consisted of an oxide coated tungsten mesh with 7 square inch of emitting surface which was heated by passing current directly through the tungsten mesh. The grids are coarse wire screen, the first of which is positioned one inch from the cathode and the second positioned one inch from the 12 within the solenoid 52; and the water jacket 54 mounted dielectric tube 14 having a large cathode 32 without focusing elements, a plate 40, two coarse screen grids 44 and 46 positioned near the cathode, and a concentric solefirst screen grid. The first grid was maintained at a positive potential with respect to the cathode and serves to accelerate electrons from the cathode. The second grid was set at a potential below that of the first grid, but experiment indicates that potential of the second grid may be varied through a wide range of voltages. The grid potentials and the strength of the magnetic field may be varied until a non-Maxwellian electron velocity distribution is obtained in the tube. The plate was positioned approximately 15 inches from the second grid. Argon gas at -a pressure of 10 microns was contained in the tube. Various other inert gases, such as xenon and krypton, proved to be satisfactory at gas pressures of from 3 to 20 microns. It is desirable to work with gases in which the collision probability decreases with increasing electron energy. The remaining tube parameters are 1 1150 gauss or 0.357 gauss/mc.

FIGURES 4 and 5 are cross section views of variations of the embodiment of my invention shown in FIGURE 1. The devices illustrated in FIGURES 4 and 5 are in all respects similar to that illustrated and specified in FIGURE 1 except for the use of ridge wave guide in place of rectangular wave guide. It is desirable to keep the overall dimensions of the amplifier as small as possible 'because this permits savings in the weight and costs of the solenoid as well as other component parts. Electromagnetic waves of longer wave lengths may be propagated through ridge wave guides than may be propagated sufficiently small so that the wave guide is not completely filled with the tube diameter.

In FIGURE 5, the solenoid is shown at .84, a water jacket at 86, ridge wave guide at 8-8, the longitudinal recesses or depressions at 90 and 92, and the plasma tube at 94. The tube 94 has been mounted off center of the Wave guide as illustrated in FIGURE 5.

I have observed that with the ridge wave guide substantially longer wave lengths may be accommodated in my amplifier utilizing the same overall dimensions and parameters as specified for the rectangular wave guide species. v6-49/ v or 6 centimeter rectangular wave guide will propagate S-band waves c'm.); ridge wave guide of similar overall cross section dimensions will propagate L-band waves cm.). No variation in the parameters specified above in connection with the rectangular wave guide species illustrated in FIGURE 1 is required for adapting ridge wave guide to my amplifier. The amplifier with ridge wave guide is operable over a broader frequency band.

FIGURE 6 illustrates a longitudinal cross section of a second embodiment of my invention adapted to operation with coaxial wave guide. A coaxial wave guide comprised of an inner conductor 1G0 and an outer conductor 182 is cut transversely, and between the ends thereof, separated by a dielectric insulating liner 104, 106, a cylindrical conducting metal tube 168 is inserted. The tube 188 is slightly smaller in diameter than the inner diameter of the coaxial outer conductor 102. The tube 1118 serves as an anode. The ends of the tube 108 are sealed by means of a dielectric disc 11%, 112 having central apertures 114 and 116, respectively. The inner coaxial wave guide conductor 1110 is connected, through the central apertures 114 and 116 by means of conductors 118 and 120, to two expandable metal bellows 122 and 124, which in turn serve as mountings for a hollow oxide cathode 126 into which a heater element 128 has been inserted. The heater is powered by leads 130 and 132 which are passed to the exterior of tube 193 through an insulator tube 134. A cylindrical screen grid 136 is mounted coaxially about the cathode 132 and connected by a lead 138 through an insulated tube fitting 140 to the exterior of the tube 188.

The necessary magnetic field is supplied by annular discs 142, 144, 146 and 148 of permanently magnetized iron. Indox V (a trade name for a permanent magnetic iron composition) has been utilized satisfactorily. The magnetic field must pass longitudinally down the tube 108 cutting transverse of the radial electron trajectories between cathode and plate. The magnetic discs are mounted outside the tube 108 but within and coaxially with the wave guide 102. The discs are polarized between their plane surfaces, the lines of Box passing parallel to cylindrical elements of the discs.

Operation of the device specified in FIGURE 6 is similar to that described for the embodiment of FIGURE 1. The cathode 126 supplies a high density of electrons which are accelerated toward the cylindrical tube and anode 188. The tube 108 contains between 3 and 20 microns pressure of a readily ionized noble gas. The permanent magnets 142, 144, 146 and 148 create a longitudinal permanent magnetic field, which, in combination with suitable screen grid potentials, creates a non- Maxwellian electron velocity distribution within the tube. Waves incident upon the plasma, in which a negative electron radiation temperature has been induced, will be stimulated and emit waves having energy greater than that of the incident waves.

Still another embodiment of my invention is illustrated in FIGURES 7 and 8 and is adapted for use with rigid coaxial wave guide. A sealed reaction tube 154 made of quartz is positioned coaxially in the center of a straight section of rigid coaxial wave guide 156. The tube 154 is held at either end by fitting into the hollow central conductors 158 and 160 of the coaxial wave guide. The wave guide section 156 is surrounded with a water jacket 162 and by an annular solenoid 164. Dielectric discs 166 and 168, which are conveniently made of polyethylene fluorides, are inserted in the wave guide 156 for supporting the central conductors.

The reaction tube 154 is elongated and contains a readily ionizable gas at between 3 and 20 microns pres sure. In the first end of the tube a cathode 170 is centrally positioned. Cathode heater leads 172 and 174 project through the end of the tube and down the inside of the central conductor 15%. A first screen grid 176 with lead 178 and a second screen grid 180 with lead 182 are mounted in spaced relationship to the grid. The leads extend through the end of the tube 154 and down the interior of the central conductor 158. It has been found convenient to space the screen grids one inch apart (in S-band) and the first grid 176 approximately one inch from the cathode 171). However, variation in these space relationships does not critically affect the operation of my invention. The second end of the tube 154 contains an anode 184 with connecting lead 186 passed through the coaxial wave guide central conductor 160.

It is convenient to curve or place an angle in the wave guide 156 adjacent each end of the amplifier tube 154 to facilitate ease'of access and to provide convenient junctions through which the various leads may be carried to the exterior of the wave guide. FIGURE 7 shows such an angled wave guide configuration, however, other convenient wave guide connections may be readily suggested and will serve as well.

Operation of the embodiment of my invention illustrated in FIGURE 7 is in all respects similar to that described above in connection with the embodiment of FIGURE 1. The cathode 17th is heated to supply a steady flow of free electrons which ionize the gas contained within the tube 154. The solenoid power, therefore the magnetic field strength, and the potential voltage applied to the screen grids 176 and 180 are adjusted so that the electron velocity distribution is non-Maxwellian. Incident electromagnetic waves propagated through the wave guide enter into the plasma within the tube 154 and there interact with the electrons and stimulate wave emulsion.

The foregoing drawings, descriptions and specifications are intended as merely illustrative of my invention and do not limit the scope nor exhaust the possible variations in my invention, the scope of which is defined in the following claims.

I claim:

1. An apparatus for increasing the energy of electromagnetic waves propagated at substantially free space velocity through a Wave guide comprising an elongated wave guide section; means for generating a magnetic field, the wave guide being mounted with the elongated section parallel to the magnetic field vector within the resultant magnetic field; an elongated dielectric container, the container being mounted longitudinally within the wave guide; means within the dielectric container for generating an electron plasma having a non-Maxwellian energy distribution; and means for introducing said electromagnetic waves at substantially free space velocity; wherewith energy is transferred from the electrons in the container to the electromagnetic waves propagated along the wave guide section.

2. A device for generating amplified electromagnetic coherent radio waves comprising a means for supplying an unfocused stream of electrons having a non-Maxwellian kinetic energy distribution; magnetic means for restraining the trajectories of the electrons; and means for conducting electromagnetic waves propagated at substantially free space velocity axially along the stream of electrons; whereby upon interaction with incident radio waves, energy in the electron stream is extracted as electromagnetic waves and propagated along the conducting means.

3. A device for amplifying radio waves propagated at substantially free space velocity through a wave guide comprising a section of Wave guide; a sealed elongated dielectric tube having first and second ends, the tube 9 being positioned to extend longitudinally within the interior of the wave guide section; an electron emitter in a first end of the dielectric tube and an anode in the second end of the tube; screen grids and means for maintaining a potential voltage thereon, the grids being in spaced relationship between the emitter and anode within the tube; a solenoid having variable current means mounted coaxially about the wave guide sections; and a quantity of ionizable gas sealed within the tube; wherewith an electron plasma is generated within the tube and confined by the magnetic field when electrons are emitted from the emitter and the solenoid current is adjusted to constrain the plasma, and the velocity distribution of the electrons in the tube is made non-Maxwellian by adjustment of the grid voltages; and means introducing radio waves which are propagated at substantially free space velocity into the wave guide section whereby the waves are amplified as they propagate along the tube and interact with the plasma.

4. A device for amplifying radio waves propagated through a wave guide at substantially free space velocity comprising a section of wave guide; a dielectric tube, the tube being positioned within the wave guide; a quantity of ionizable gas within the tube; an electron source positioned within the tube; anode means mounted within the tube in spaced relationship to the electron means; grid electrode means mounted in the tube intermediately between the electron source and the anode means; and magnetic means mounted exterior of the wave guide for maintaining a constant magnetic field, the field vector of which is oriented axially along the direction of propagation of waves within the interior of the wave guide section; wherein electrons are emitted from the electron source and are accelerated toward the anode through the gride electrode means and the ionizing gas, thereby creating a non-Maxwellian electron velocity distribution within an electron plasma which is constrained by the magnetic field, and means introducing radio waves at substantially free space velocity which propagate through the wave guide and interact with the constrained electron plasma and derive energy from the interaction which increases the wave intensity.

5. The device of claim 4 comprised of rectangular wave guide section and coaxially mounted solenoid magnetic means, in combination with means for passing liquid coolant between the wave guide and the solenoid magnetic means.

6. The device of claim 5 comprised of ridge wave guide I section in place of rectangular wave guide section.

7. The device of claim 5 comprised of coaxial wave guide section in place of rectangular wave guide section.

through a wave guide at substantially free space velocity comprising a section of wave guide; an elongated sealed dielectric tube, the tube being positioned within the wave guide section; a quantity of ionizable gas within the tube; an electron source positioned at a first end of the tube; anode means mounted within the tube at a second end of the tube; grid electrode means mounted within the tube intermediate between the electron source and the anode; a torroidal cylindrical solenoid mounted coaxially about the wave guide section; and a cylindrical hollow conduit adapted to pass liquid coolant mounted within the solenoid and coaxially about the wave guide section; wherein electrons are emitted from the electron source and accelerated within the magnetic field through the grid means and through the ionizable gas to form a non- Maxwellian electron velocity plasma within the tube, and means introducing said radio waves at substantially free space velocity into the wave guide whereby the radio waves propagated through the wave guide interact with the plasma and, by stimulated emission by the electrons, amplify the radio waves.

References Cited by the Examiner UNITED STATES PATENTS 2,833,955 5/ 1958 Marchese 315-3.5 2,840,757 6/1958 Dench 315-393 3,099,768 7/ 1963 Anderson. 3,111,604 11/1963 Agdur 330-41 FOREIGN PATENTS 671,858 5/1962 ,Great Britain.

OTHER REFERENCES magnetics and Fluid Dynamics of Gaseous Plasma, 1962,

Hutter et al. Article, Traveling-Wave Tubes, pp. 23-25,

71, Radio-Electronic Engineering, April 1954.

ROY LAKE, Primary Examiner.

NATHAN KAUFMAN, Examiner.

F. D. PARIS, Assistant Examiner. 

1. AN APPARATUS FOR INCREASING THE ENERGY OF ELECTROMAGNETIC WAVES PROPAGATED AT SUBSTANTIALLY FREE SPACE VELOCITY THROUGH A WAVE GUIDE COMPRISING AN ELONGATED WAVE GUIDE SECTION; MEANS FOR GENERATING A MAGNETIC FIELD, THE WAVE GUIDE BEING MOUNTED WITH THE ELONGATED SECTION PARALLEL TO THE MAGNETIC FIELD VECTOR WITHIN THE RESULTANT MAGNETIC FIELD; AN ELONGATED DIELECTRIC CONTAINER, THE CONTAINER BEING MOUNTED LONGITUDINALLY WITHIN THE WAVE GUIDE; MEANS WITHIN THE DIELECTRIC CONTAINER FOR GENERATING AN ELECTRON PLASMA HAVING A NON-MAXWELLIAN ENERGY DISTRIBUTION; AND MEANS FOR INTRODUCING SAID ELECTROMAGNETIC WAVES AT SUBSTANTIALLY FREE SPACE VELOCITY; WHEREWITH ENERGY IS TRANSFERRED FROM THE ELECTRONS IN THE CONTAINER TO THE ELECTROMAGNETIC WAVES PROPAGATED ALONG THE WAVE GUIDE SECTION. 